Proline is an amino acid needed for the production of collagen and cartilage. It keeps muscles and joints flexible and helps reduce sagging and wrinkling that accompany UV exposure and normal aging of the skin. Proline helps the body break down proteins for use in creating healthy cells in the body. It is absolutely essential to the development and maintenance of healthy skin and connective tissues, especially at the site of traumatic tissue injury. Proline and lysine (another one of the amino acids that is important to protein synthesis) are both needed to make hydroxyproline and hydroxylysine, two amino acids that form collagen. Collagen helps to heal cartilage and to cushion the joints and vertebrae. For this reason, proline supplementation may prove beneficial for treatment of conditions such as osteoarthritis, persistent soft tissue strains, and chronic back pain. The body needs proline to maintain muscle tissue as well. Decreases in proline levels have been noted in prolonged endurance runners and others following prolonged exercise.